(a) Field of the Invention
This invention relates to a jacking apparatus for moving loads along a rail mounted on a horizontal base, such as on the deck of a floating platform.
(b) The Prior Art
Prior art jacking devices for moving heavy loads along a rail generally comprised sleds with large hydraulic cylinders connected to claws which successively engaged holes in a rail, see for example, U.S. Pat. No. 4,007,915 and the references cited therein.
The main drawbacks of such known devices are due to the fact that: they are massive and of relatively inflexible design, they require many accurately machined and located rail slots, they lack flexibility in operation, for example, their direction of motion is not easily reversible, and they require relatively complex auxiliary equipments to assist in their operation.
Moreover, in those jacking devices which must employ pairs of laterally-spaced hydraulic cylinders, when one cylinder of the pair becomes inoperative, or when the forces produced by the individual cylinders become unbalanced, either such jacking devices become inoperative or they lose some of their effectiveness.
Accordingly, the main objects of the present invention are to simplify the construction and cost of such known jacking devices, and to employ only single slots longitudinally spaced along the rail. The slots need not be accurately spaced apart. It is a further object to provide jacking devices which are easy to assemble and to dis-assemble, which occupy a minimum of space, which require a minimum of material, thereby making them relatively lightweight, which require no pairs of balanced cylinders, which require a minimum of joining operations during their construction, and which require simple means for changing the direction of motion of the jacking device. Other objects will become apparent from the specification when considered together with the drawings.